The present invention relates to a speed up device for a bicycle, and the main body of said device is formed by shaping an opening on the surface of a triangle shape corresponding to an opposite side of the rotating direction of the wheel and having a cross section of an almost triangular shape hollow chamber and a bottom plate and a reinforcing plate being detachably installed thereon, and when the main body is mounted on the axle, the bottom plate and the reinforcing plate are removed, and while the hollow chamber is in compressed condition, it is fitted into the space formed by the axle and the spokes of the wheel, and then the reinforcing plate and the bottom plate are installed on the speed up body, and the speed up body is arranged to be assembled and installed easily in the space surrounded by the axle and spokes of the wheel and then the swelling volume of the air is greatly increased, producing the increased thrust to the bicycle.
Heretofore, as a speed up device for a bicycle which is designed to increase the speed by receiving a head wind or a tail wind, there is a Japanese utility model registration No. 1,148,681, but this invention is constructed in such a way that a cover plate inclined toward the rear direction is formed over from almost the center portion of the back plate to the rear portion, and a space portion whose front surface is open is provided, and this device is fixed to the spokes of the wheel by means of bolts.
However, this speed up device was constructed in such a way that the device was installed in projecting form on the outer surface of the spokes of the wheel, and for this reason, in order to avoid danger in the area projecting outward of the wheel, the speed up device had to be constructed in small size. As a result, the volume of the speed up device receiving the wind power was small, and as a result, a large number of speed up devices must be installed on both surfaces of the wheel. Such installation was not satisfactory.